Three-dimensional semiconductor packages become essential for a higher density and capacity. The 3D semiconductor packaging technology is by thinning semiconductor chips, and stacking them in multilayer structure while providing through-silicon via (TSV) interconnects. Fabrication of such packages requires the steps of thinning a substrate having a semiconductor circuit formed therein by grinding its non-circuit forming surface or back surface, and forming TSV and electrodes on the back surface. In the prior art, prior to the step of grinding the back surface of a silicon substrate, a protective tape is attached to the surface of the substrate opposite to the surface to be ground for preventing the wafer from breakage during the grinding step. Since the protective tape is based on an organic resin film, it is flexible, but has insufficient strength and heat resistance to withstand the TSV forming step and the step of forming interconnects on the back surface.
It is then proposed to bond a semiconductor substrate to a support of silicon or glass, for example, via an adhesive layer. The resulting system is sufficient to withstand the steps of grinding the back surface and forming TSV and electrodes on the back surface. The adhesive layer for bonding the substrate to the support is critical for this system. The adhesive layer must bond the substrate to the support without leaving gaps, be durable enough to withstand the subsequent steps, and eventually allow the thin wafer to be readily released from the support. The adhesive layer is referred herein to as “temporary adhesive layer” since it is finally removed.
While the temporary adhesive layers and removal thereof are well known, Patent Document 1 discloses a layer of an adhesive composition comprising a heat melting hydrocarbon compound, wherein the layer can be bonded and released in the heat molten state. This technology is simple because of mere thermal control, but is applicable to a limited range because of instability at high temperatures in excess of 200° C.
Patent Document 2 discloses the use of a silicone pressure-sensitive adhesive as the temporary adhesive layer. A substrate is bonded to a support via an addition curable silicone adhesive composition. On removal, the assembly is immersed in an etching solution capable of dissolving or decomposing the silicone resin, whereby the substrate is separated from the support. This method takes a very long time for removal and is difficult to apply to the commercial manufacture process.
On the other hand, Patent Document 3 describes an adhesive layer containing a photo-absorptive substance. The adhesive layer is separated from the support by irradiating high-intensity light to the adhesive layer for decomposing it. Although the processing time per substrate upon removal of the substrate from the support is short, this method must use a metal compound for converting the irradiated light to heat, leaving a risk of contaminating the substrate with the metal.